1. Field of the Invention
The present invention relates to a hot water supply apparatus having a hot water supply temperature sensor for temperature control and a hot water supply temperature sensor for comparison.
2. Description of the Related Art
In a hot water supply apparatus for controlling a temperature of hot water supplied to a hot-water supplying terminal based on a temperature detected by a hot-water supply temperature sensor, when a temperature detection accuracy is deteriorated due to abnormality in the hot-water supply temperature sensor, a deviation occurs between the temperature detected by the hot-water supply temperature sensor and a set temperature. As a result, there is a possibility that hot water having a higher temperature than the set temperature is supplied to the hot-water supplying terminal. From the above point of view, a hot water supply apparatus provided with another hot-water supply temperature sensor for determining whether the hot-water supply temperature sensor for temperature control is abnormal or not by comparison is known. (For example, Japanese Unexamined Patent Publication No. 2004-202122) According to the hot water supply apparatus, when a difference between the temperature detected by the hot-water supply temperature sensor for comparison and the temperature detected by the hot-water supply temperature sensor for temperature control is larger than a predetermined value, abnormality of the hot-water supply temperature sensor for temperature control is determined, and whereby supply of hot water can be stopped.
FIG. 5 is a schematic configuration diagram showing a conventional hot water supply apparatus provided with a hot-water supply temperature sensor for comparison. The hot water supply apparatus 9 has a cold-water pipe L1 for guiding cold water supplied from a water supply pipe to a mixed-water pipe L5 which will be described later, a hot-water pipe L2 for guiding hot water supplied from a hot-water generator such as a heat exchanger to the mixed-water pipe L5, and the mixed-water pipe L5 for guiding the cold water and the hot water to a hot-water supplying terminal P such as a shower or a faucet.
To a merging part of the cold-water pipe L1 and the hot-water pipe L2, a mixing valve 95 as a temperature control unit capable of adjusting supply proportions of the cold water and the hot water to the mixed-water pipe L5 is connected. By controlling the supply proportions by the mixing valve 95 based on a temperature detected by a hot-water supply temperature sensor 98a for temperature control which will be described later, the temperature of hot water supplied to the hot-water supplying terminal P is adjusted.
The mixed-water pipe L5 is provided with the hot-water supply temperature sensor 98a for temperature control for detecting the water temperature in the mixed-water pipe L5, a hot-water supply temperature sensor 98b for comparison, and a hot-water shutoff valve 99 capable of shutting off the supply of hot water to the hot-water supplying terminal P.
Further, a control circuit C9 for executing an operation of supplying hot-water to the hot-water supplying terminal P is assembled in the hot water supply apparatus 9. The mixing valve 95, the hot-water supply temperature sensor 98a for temperature control, the hot-water supply temperature sensor 98b for comparison, and the hot-water shutoff valve 99 are electrically connected to the control circuit C9.
The control circuit C9 includes, although not shown, a hot-water supply temperature control circuit for controlling operation of the mixing valve 95 based on the temperature detected by the hot-water supply temperature sensor 98a for temperature control, a sensor abnormality determining circuit for determining sensor abnormality when the difference between the temperature detected by the hot-water supply temperature sensor 98a for temperature control and the temperature detected by the hot-water supply temperature sensor 98b for comparison is larger than a predetermined value, and a hot-water supply inhibiting circuit for forcibly closing the hot-water shutoff valve 99 when the sensor abnormality is determined.
In the hot water supply apparatus, when a hot-water supply key in a remote controller R connected to the control circuit C9 via a communication cable is depressed, first, a sensor abnormality determining circuit determines whether the difference between the temperature detected by the hot-water supply temperature sensor 98a for temperature control and the temperature detected by the hot-water supply temperature sensor 98b for comparison is equal to or less than a predetermined value (for example, 1 K).
When the detection temperature difference is equal to or less than the predetermined value, the mixing valve 95 is controlled by a hot-water supply temperature control circuit, and the supply proportions of cold water and hot water to the merging part is adjusted so that the temperature detected by the hot-water supply temperature sensor 98a for temperature control is matched with the set temperature of the remote controller R.
On the other hand, in a case where the temperature detection accuracy of the hot-water supply temperature sensor 98a for temperature control is deteriorated, the detection temperature difference may exceed a predetermined value. In such a case, when adjustment for decreasing the supply proportion of the cold water to the merging part is performed based on the temperature detected by the hot-water supply temperature sensor 98a for temperature control, there is a possibility that hot water having a higher temperature than the set temperature can be supplied to the hot-water supplying terminal P. Consequently, abnormality of the hot-water supply temperature sensor is determined, and the hot-water shutoff valve 99 is closed by the hot-water supply inhibiting circuit.
As a result, supply of a high-temperature hot water to the hot-water supplying terminal P is stopped, so that it does not cause discomfort to a user.
In the conventional hot water supply apparatus, however, when it is determined that the hot-water supply temperature sensor for temperature control is abnormal, supply of hot water is stopped forcibly. Consequently, the hot water supply apparatus cannot be used until the hot-water supply temperature sensor for temperature control is replaced, thereby resulting in poor convenience.